The present invention relates to a tap for an optical fiber, networks usable therewith, and optimum geometries therefor.
In recent years significant efforts have been directed towards devising methods and apparatuses for tapping optical fibers for distribution networks, and although many of the methods proposed show interesting experimental results, a common disadvantage of all prior art proposals is that the methods and apparatuses suggested are either too complex in design to be cost effective, are unduly difficult to install, are not sufficiently optically efficient, or create system hazards such as undue strain on an optical fiber which causes premature failure thereof.
Goell et al., U.S. Pat. No. 3,982,123 discloses various methods for tapping an optical fiber through a side thereof, these methods requiring that either a fiber coating, or a fiber coating and its cladding be removed. This has proved disadvantageous when used in conjunction with optical fibers including glass cores and glass claddings since removal of the coating and/or the fiber cladding exposes either the glass cladding or the glass core to OH ions in the atmosphere which quickly degrades the strength of the optical fiber.
Miller, G. B. U.S. Pat. No. 2,126,749B discloses a method for tapping an optical fiber while leaving its coating intact, the method comprising disposing the optical fiber within a transparent light pipe, creating a bend in the optical fiber either upstream of the light pipe or within the light pipe, and disposing an optical detector at a remote end of the light pipe. Miller further teaches that the fiber be bent about a radius of curvature of less than 1 mm, and that the fiber bend subtend an angle of greater than 10.degree.. These teachings are disadvantageous since a bend radius of less than 1 mm is extremely detrimental to the life of an optical fiber, even if its coating is left intact, thus rendering taps constructed as such undesirable for distribution networks wherein the optical fiber bend profile remains static over time. In addition, such a small bend radius also puts the fiber under sufficient strain such that its buffer coating tends to relax over time which changes the bend profile and hence changes the optical coupling efficiency of the tap with time. Finally, the Miller tap is difficult to make in quantities in a cost efficient manner, and also very craft sensitive to install.
Dakin et al., "Experimental Studies into the Non-Invasive Collection and Distribution of Data on a Fiber-Optic Monomode Bus" describes a method for sequentially tapping an optical fiber in series by bending a highway bus fiber about an arc, and disposing a polymer tapping fiber on an outside bend surface of the highway fiber, the polymer fiber having a 200 micron wide flat surface machine formed thereon to facilitate optical coupling with the bus fiber. Though Dakin et al. specifies favorable results, the construction of the taps proposed is extremely complex and difficult to make and install so as to achieve repeatable results.